正交分頻多工系統通訊方式為E-UTRAN所採用，先前有一篇研究名為「正交分頻多工系統下適應型天線陣列運用虛擬載波進行干擾抑制」可降低同頻強干擾，進而達到良好的表現。該篇研究是基於特徵值分析方法，並在一個正交分頻多工符碼區間內，利用非零值之資訊子載波來估測發送訊號加上干擾及雜訊之空間關係矩陣；以及利用零值之虛擬子載波來估測干擾及雜訊之空間關係矩陣。進而波束成型權重向量的解答就是兩個評估空間矩陣之最大廣義特徵向量。
上述方法看似完美，但不幸的是它的表現會隨著子載波總數增加而變的非常差。在此篇論文內，我們不但發現了錯誤率表現變差的原因，並想到了利用閒置資訊子載波去改善空間關係矩陣的評估結果。此外，本篇論文亦提出了二維區段估測方法來解決上述表現變差之問題，甚至於子載波總數達到2048。而此子載波數目係在E-UTRAN標凖中最大子載波數。最後，本篇論文藉由一連串的實驗，進行發展出如何決定在頻域及時域上之區段大小的方法。

The Orthogonal frequency division multiplexing (OFDM) communication system is adopted for transmission by Evolved-Universal Terrestrial Radio Access Network (E-UTRAN). A former research, “Adaptive Antenna Arrays for Interference Cancellation in OFDM Communication Systems With Virtual Carriers”, can cancel strong co-channel interferences to achieve competitive performances. This research is based on Eigen-analysis and it estimates the spatial correlation matrix of signal-plus-interference-plus-noise by choosing samples from information subcarriers (nonzero-value) and estimates the spatial correlation matrix of interference-plus-noise by selecting samples from virtual subcarriers (zero-value) in one OFDM symbol duration. The solution of the beamforming weight vector by Eigen-analysis is the “largest” generalized eigenvector corresponding to the estimated matrix pencil.
Unfortunately, those schemes look perfect but their performances become worse as the increasing of subcarriers. In this thesis, we find out the reason for bad performances and utilize the “idle data subcarriers” to enhance the estimation of spatial correlation matrix. Besides, we propose the “2D-grouping” method to improve the bad performance problem even the subcarrier number equals to 2048 that is the maximal number of subcarriers in E-UTRAN. Finally, this thesis also develops the scheme to decide the grouping range in frequency and time domains by a serious of experiments.

[1]L. J. Cimini, Jr., “Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing,” IEEE Trans. Commun., vol. COM-33, no. 7, pp. 529–540, Jul. 1985.
[2]R. V. Nee et al., “New high-rate wireless LAN standards,” IEEE Commun. Mag., vol. 37, no. 12, pp. 82–88, Dec. 1999.
[3]J. Chuang and N. Sollenberger, “Beyond 3G: Wideband wireless data access based on OFDM and dynamic packet assignment,” IEEE Commun. Mag., vol. 38, no. 7, pp. 78–87, Jul. 2000.
[4]Part II: Wireless LAN Medium Access Control (MAC) and Physical Layer(PHY) Specifications: High-Speed Physical Layer in the 5 GHz Band, IEEE Std. 802.11a-1999, 1999.
[5]Part II: Wireless LAN Medium Access Control (MAC) and Physical Layer(PHY) Specifications: Further Higher Data Rate Extention in the 2.4 GHz band (Amendment to IEEE Std. 802.11, 1999 ed. Reaff 2003), IEEE Std. 802.11g-2003, 2003.
[6]D. Bartolome and A. I. Perez-Neira, “MMSE techniques for space diversity receivers in OFDM-based wireless LANs,” IEEE J. Sel. AreasCommun., vol. 21, no. 2, pp. 151–160, Feb. 2003.
[7]M. Budsabathon, Y. Hara, and S. Hara, “Optimum beamforming for pre-FFT OFDM adaptive antenna array,” in Proc. WCNC, Mar. 2003, vol. 1, pp. 32–37.
[8]S. Kapoor, D. J. Marchok, and Y.-F. Huang, “Adaptive interference suppression in multiuser wireless OFDM systems using antenna arrays,” IEEE Trans. Signal Process., vol. 47, no. 12, pp. 3381–3391, Dec. 1999.
[9]Y. Li and N. R. Sollenberger, “Adaptive antenna arrays for OFDM systems with cochannel interference,” IEEE Trans. Commun., vol. 47, no. 2,pp. 217–229, Feb. 1999.
[10]A. A. Hutter, J. S. Hammerschmidt, E. de Carvalho, and J. M. Cioffi, “Receive diversity for mobile OFDM systems,” in Proc. IEEE Wireless Commun. Netw. Conf., Sep. 2000, vol. 2, pp. 707–712.
[11]K.-K. Wong, R. S.-K. Cheng, K. B. Letaief, and R. D. Murch, “Adaptive antennas at the mobile and base stations in an OFDM/TDMA system,” IEEE Trans. Commun., vol. 49, no. 1, pp. 195–206, Jan. 2001.
[12]H. Bolcskei, R. W. Heath, Jr., and A. J. Paulraj, “Blind channel identification and equalization in OFDM-based multiantenna systems,” IEEE Trans. Signal Process., vol. 50, no. 1, pp. 96–109, Jan. 2002.
[13]Y. F. Chen and C. S. Wang, “Adaptive antenna arrays for interference cancellation in OFDM communication systems with virtual carriers,” IEEE Trans. Veh. Technol., vol. 58, no 4,pp. 1837-1844, Jul. 2007.
[14]C. Y. Liu, Y. F. Chen, C.P Li, ”Blind Beamforming Schemes in SC-FDMA Systems With Insufficient Cyclic Prefix and Carrier Frequency Offset,” IEEE Trans. Veh. Technol., vol. 58, no.9, pp. 4848-4859, May 2009.
[15]Z. Cao, U. Tureli, Yu-Dong Yao, and P. Honan, “Frequency synchronization for generalized OFDMA uplink,” in Proc. IEEE Global Telecomm. Conf., Nov. 2004, vol.2, pp. 1071-1075.
[16]M. D. Zoltowski and J. Ramos, “Blind multi-user access interference cancellation for CDMA based PCS/cellular using antenna arrays,” in Proc. IEEE Int. Conf. Acoust., Speech, Signal Process., May 1996, vol. 5,pp. 2730–2733.
[17]T. F. Wong, T. M. Lok, J. S. Lehnert, and M. D. Zoltowski, “A linear receiver for direct-sequence spread-spectrum multiple-access systems with antenna arrays and blind adaptation,” IEEE Trans. Inf. Theory, vol. 44,no. 2, pp. 659–676, Mar. 1998.
[18]“3GPP Technical Specification 36.213 version 12.3.0 Release 12,” LTE; Evolved Universal Terrestrial Radio Access (E-UTRA), Physical layer procedures [online] Available: http://www.3gpp.org.
[19]M. Morelli and U. Mengali, “A comparison of pilot-aided channel estimation methods for OFDM systems,” IEEE Trans. Signal Process., vol. 49,no. 12, pp. 3065–3073, Dec. 2002.